Hybrid silicon quantum dot lasers (hsqdl) with reduced thermal resistance

Abstract

Hybrid silicon quantum dot laser (HSQDL) structure including an optical waveguide of a first width, a mesa of a second width and a current channel of a third width that is smaller than the second width. In some examples, the third width is only slightly larger than the first width to narrowly confine electrical current directly over the optical waveguide while the third width is significantly larger than the first width to efficiently transport heat away from the optical gain medium. While the current channel has a low electrical resistivity, other regions of the mesa contributing to the third width have a higher electrical resistivity. In some examples, an implant process is practiced to increase electrical resistivity.

What is claimed is: 
     
         1 . A laser source, comprising:
 a planar optical waveguide comprising silicon; and   a mesa comprising a quantum dot (QD) material over the planar optical waveguide, wherein the mesa has a first width, and wherein electrical resistivity within at least one material layer of the mesa varies over the first width.   
     
     
         2 . The laser source of  claim 1 , wherein the electrical resistivity of the at least one material layer is lower over a second width spanning a central portion of the mesa, and higher proximal to a sidewall of the mesa. 
     
     
         3 . The laser source of  claim 2 , wherein the optical waveguide has a third width, smaller than the second width. 
     
     
         4 . The laser source of  claim 2 , wherein:
 the optical waveguide is crystalline silicon and has a width less than 1 μm;   the first width is at least 10 μm; and   the second width is less than 6 μm.   
     
     
         5 . The laser source of  claim 2 , wherein the at least one material layer comprises a p-type material layer, and wherein the electrical resistivity over the second width within the p-type material layer is at least two orders of magnitude lower than the electrical resistivity within the p-type material layer beyond the second width. 
     
     
         6 . The laser source of  claim 5 , wherein the first width is at least 20 μm. 
     
     
         7 . The laser source of  claim 5 , wherein:
 the p-type material layer is a crystalline III-V material layer of a first thickness; and   the p-type material layer comprises two electrically resistive regions adjacent to opposite sides of the central portion, the two resistive regions each comprising at least half the first thickness.   
     
     
         8 . The laser source of  claim 7 , wherein the two resistive regions each have a width of at least 1 μm. 
     
     
         9 . The laser source of  claim 7 , further comprising a contact metallization feature over the mesa, the contact metallization spanning the second width and over at least a majority of two the resistive regions. 
     
     
         10 . The laser source of  claim 2 , further comprising:
 a contact metallization feature over the mesa, the contact metallization feature having a width between the first width and the second width; and   an interconnect metallization feature over, and in direct contact with, the contact metallization feature, wherein the interconnect metallization feature has a different chemical composition than the contact metallization feature and has a thickness of at least 8 μm.   
     
     
         11 . A photonic integrated circuit (PIC), comprising:
 a plurality of optical waveguides extending over a crystalline silicon substrate; and   a plurality of hybrid silicon-quantum dot lasers (HSQDLs), wherein each of the HSQDLs comprises:
 a stack of III-V semiconductor material over an active portion of a corresponding one of the optical waveguides, wherein:
 the stack comprises a QD material layer between a p-type material layer and an n-type material layer; 
 the stack has a first width, larger than a width of the active portion of the optical waveguide; and 
 electrical resistivity of one of the p-type material layer or n-type material layer varies over the first width. 
 
   
     
     
         12 . The PIC of  claim 11 , wherein the electrical resistivity is lower over a second width spanning a central portion of the stack, and higher within an edge portion proximal to a sidewall of the stack. 
     
     
         13 . The PIC of  claim 12 , wherein:
 each of the optical waveguides is crystalline silicon and has a width less than 1 μm;   the first width is at least 10 μm; and   the second width is less than 5 μm.   
     
     
         14 . The PIC of  claim 11 , wherein each of the HSQDLs is to output at a different center wavelength. 
     
     
         15 . A method comprising:
 forming a hybrid structure comprising a III-V material stack over an optical waveguide comprising predominantly silicon, wherein the III-V material stack comprises a quantum dot (QD) material layer over a first impurity doped material layer and under a second impurity doped material layer;   increasing electrical resistivity of the second impurity doped material layer outside a first region of the III-V material stack directly over the waveguide, or lowering electrical resistivity of the second impurity doped material layer within the first region of the III-V material stack;   forming a first contact to the first impurity doped material layer; and   forming a second contact to the second impurity doped material layer.   
     
     
         16 . The method of  claim 15 , wherein increasing the electrical resistivity of the second impurity doped material layer comprises implanting one or more species into the second impurity doped material layer. 
     
     
         17 . The method of  claim 16 , wherein implanting the one or more species induces crystal lattice damage. 
     
     
         18 . The method of  claim 17 , wherein the one or more species comprises a proton or a helium ion. 
     
     
         19 . The method of  claim 17 , further comprises applying an implant mask over the first region prior to implanting the one or more species. 
     
     
         20 . The method of  claim 15 , further comprising forming a mesa by etching at least partially through both the second impurity doped material layer and the QD material layer, wherein the mesa comprises sidewalls located beyond the first region.